Most people who have been involved in regular resistance training for several years will confirm that muscle injuries are common. They are not, however, inevitable and whether you experience any type of muscle injury depends on several factors. The foremost factor related to muscle injuries is using poor form. Despite the plethora of information available over the Internet and in various print media, poor form dominates in most of those who train today. At the two gyms that I train at, I would estimate that at least 99% of those who exercise at these gyms have no idea of what constitutes good form. Not only does using poor exercise form blunt muscle gains, but it also places muscles and joints in precarious positions that could easily lead to injuries. Another common cause of muscle injuries is not warming up properly. Jumping right into lifting without any type of warm-up can easily result in a muscle injury. Contrary to popular belief, it is neither necessary nor desirable to engage in extended stretching prior to training as a means of warming up. Research shows that excessive stretching prior to training weakens the muscle, promoting as great as a 24% drop in muscular strength. Ironically, that drop in strength from excessive pre-workout stretching can itself promote muscle injuries. The best way to warm up is simply to do one or two light sets using higher repetitions. I follow this advice myself. My first set on any exercise involves using very light weight and doing 20 to 30 reps. I then move on to heavier weight on succeeding sets.
Still, even using perfect exercise form it's easy to incur a muscle injury. This can range from minor muscle strains to tears in the muscle. The good news is that muscle has an extensive blood system and this blood perfusion promotes faster healing. Contrast that with tendon or connective tissue injuries. Connective tissue, which is what joints and tendons are comprised of, has poor blood circulation within the tissue. This lack of relative blood circulation results in far longer healing times compared to muscle injuries. One of the worst things anyone can do is continue to train a muscle or a joint area after it has been injured. Doing so just makes the injury worse. I've been guilty of that myself when I was younger and competing in bodybuilding contests. I was loath to rest any injured muscle because I thought that not training it would result in muscle atrophy. While that may be true, training an area that is already injured won't help the healing process and is likely to make a bad situation worse.
As you age, the chances of incurring a muscle injury increase. One aspect of aging that is common to all is that muscles require more recuperation between training sessions. In practical terms, this means less training frequency. If you check out YouTube videos . . .